This invention relates to refrigerated storage and subsequent oven processing of food and more particularly it relates to such processing in oven appliances which are cooled and heated by a liquid thermal exchange fluid.
This invention and the inventions of the above cross-references relate to various aspects of a novel system of domestic appliances wherein heat is exchanged between a plurality of appliances and a plurality of thermal reservoirs by forced circulation of a liquid phase thermal exchange fluid between a heat exchanger in an appliance selected for operation and a heat exchanger in a thermal reservoir selected for heating or cooling the thermal exchange fluid.
A thermal reservoir assembly, commonly shared by the appliances, comprises the thermal reservoirs each heating or cooling thermal exchange fluid in a reservoir heat exchanger which is connected through a pump to a supply and return main pair to which the appliances connect. Included among the thermal reservoirs are a hot reservoir maintained above oven cooking temperatures by a heat storing material having a large heat of crystallization at a high temperature, a cold reservoir maintained below refrigerator and freezer temperatures by a heat storing material having a large heat of fusion at a low temperature, and a heat sink at outdoor ambient temperature.
An appliance heat exchanger connects to the plurality of supply and return main pairs through a pair of selector valves. An appliance regulator valve then modulates flow of thermal exchange fluid from the selected supply and return main pair. Temperature within an appliance is regulated precisely over a range of cooking and freezing temperatures by a programmed operation of the selector and regulator valves.
The thermal reservoirs are charged at moderate power levels during off-peak hours and are able to provide large quantities of thermal energy during periods of peak appliance use. Energy conservation is enhanced by use of the ambient outdoor air heat sink to moderate appliance temperature during transitions between hot and cold to reduce thermal loading of the hot and cold reservoirs.
Some appliance units may be connected to only one of the supply and return main pairs to provide either heating or cooling. A sink appliance supplying hot water for instant hot beverages which regulates flow of hot thermal exchange fluid is an example. But the marginal cost of selector valves to connect an appliance to all of the supply and return main pairs is small. Accordingly, it is economical for an appliance of this system to provide both heating and cooling capability together with temperature moderation by ambient air.
Domestic unattended cooking is attained by refrigerated storage of food for subsequent programmed processing and completion at a specified time. Such refrigerated storage and cooking has been practiced in vending, catering, and restaurant applications, but has been too complex or too specialized for use in homes. One process, for example, transfers a food package from a cold zone to a hot zone by conveyer means.
In another process more adaptable to a smaller scale disclosed by T. S. Shevlin in U.S. Pat. No. 3,608,627, a refrigerator contains a plurality of insulated food containers or casseroles which are heated automatically and individually by heating elements. The system is still complex, however, in that a refrigeration unit, heating elements, and separate controllers are required. Further, the range of cooking processes in a casserole type container having food in thermal contact with a heat source is more limited than that of an oven configuration where food is heated by air convection. An oven, for example, can bake bread as well as heat casseroles.
Oven type structures having both refrigeration units and heating elements are used in laboratory testing applications. The oven, comprising an insulated compartment with heating and cooling means, has a heat exchanger to receive a controlled flow of a refrigerant fluid for cooling and it also has electrical heating elements which may be controlled to provide high oven temperatures. Even if such an oven unit shared with other units a common refrigerant source, an oven unit with both heat exchanger and heating element structures each with their control means would still be inappropriately complex and costly if adapted to domestic food processing functions.
In yet another process for refrigerating and subsequently cooking food disclosed by F. I. Bemiss et al. in U.S. Pat. No. 3,242,980, supply and return ducts provide cold and hot air for portable insulated food cabinets. Air at temperatures regulated by valves flows from a supply duct, over food, and to a return duct. System features of shared sources of heat and cold and simple food cabinet structure contribute to system economy. Entrainment of cooking odors and vapors in circulating hot air, however, would be undesireable in diverse domestic cooking.
Ovens conventionally provide a hot atmosphere in which food is immersed for such cooking functions as roasting or baking. The temperature within the oven is normally sufficient to result in desirable nonreversible alterations of food properties by thermal processes which occur over relatively short exposure times, typically of about an hour. Such alterations of food properties are based on molecular changes, such as carbonization in surface browning, which occur at reasonable rates at higher temperatures, typically above 275.degree. F.